It is well recognized in the art that the full efficacy of a given organic herbicide is not generally attained without the inclusion of various adjuvants, an adjuvant being broadly defined as any substance which enhances the effectiveness of the herbicide. Thus, for example, through proper formulation with an activity-increasing adjuvant, the control of a particular plant species by an herbicide can be greatly augmented. Such an activity-increasing adjuvant does not generally have biological activity on its own but only brings out the activity of the herbicide.
An example of the aforementioned activity-increasing adjuvants is the class of surfactants known as silicone glycols. These liquids have been shown to enhance the efficacy of various herbicides. L. L. Jansen (Weed Science, v. 21, pages 130-135, Mar. 1973) examined the effect of adding various silicone glycol adjuvants to different herbicides and reported that these adjuvants were superior to a standard organic surfactant in eight plant species. In this study, cationic amino silicone surfactants were also evaluated, but found to be less effective than the organic material. In any event, no specific structures of the silicone compounds were provided in this paper.
Great Britain Pat. No. 1,255,249 to Dow Corning Corporation, published Dec. 1, 1971, again discloses herbicide compositions employing silicone glycol copolymers. Here, general utility of a large number of adjuvants is professed, as exemplified by two generic silicone glycol formulas which embrace structures having both diorganosiloxane units and alkyl-glycol siloxane units. There is also provided a wide-ranging list of suitable herbicides. This reference, however, provides little direction to those skilled in the art as to which particular silicone glycol structures are to be advantageously combined with specific herbicides, save for two examples employing a triazine herbicide in conjunction with an adjuvant having 1.8 siloxy units and bearing a glycol chain having 12 ethylene oxide units.
In addition to the herbicidal enhancement provided by the activity-increasing adjuvants discussed above, it is often important that herbicide formulations retain a significant degree of activity when plants treated therewith are exposed to rain shortly after application, this being a definition of the degree of "rainfastness." This is particularly critical for water-soluble foliar-applied herbicides, such as glyphosate salts, which may be washed away by rainfall occurring within about six hours of application. Typically, this problem is currently addressed by inclusion of another class of adjuvants in the herbicide formulation, namely sticking agents (see, for example, page 6 of Adjuvants for Herbicides, Weed Science Society of America, Champaign, IL, 1982). The main function of these materials, as the appelation implies, is to impart an increased measure of adhesion of the herbicide composition to plant foliage and thus reduce premature washing away should precipitation occur after the plants are sprayed. The sticking agents are usually polymeric compounds which are generally water-soluble and tacky in nature.
Neither Jansen nor British Pat. No. 1,255,249 addresses the issue of rainfastness nor does any reference suggest to those of ordinary skill in the art the use of applicants' particular silicone glycol-silicone alkane terpolymers to provide enhanced activity in conjunction with particular herbicides.